The voice of the Yorkshire Ripper is about to be heard on television for the first time.

Peter Sutcliffe's Bradford accent will be broadcast in a documentary which examines the bizarre phenomenon of women who have become obsessed with the murderer and struck up relationships with him while he languishes inside his prison cell.

The lorry driver from Heaton was jailed 20-years ago this month for murdering 13 women and attacking seven more.

His reign of terror began in Leeds in 1975 when the mutilated body of Wilma McCann was discovered in a field. His attacks stretched from Bradford and Keighley to Manchester and Halifax - one of his victims was killed just 500 yards away from Bradford police headquarters in the city centre.

But dozens of women have written to him in jail, many becoming obsessed with him.

The BBC documentary explores the reasons for their fascination with one of the country's worst killers and focuses on three women's relationships with him. Sutcliffe's voice - which has never before been broadcast - will be heard on a tape which was sent to one of his admirers. Many of his letters and artwork will also be included.

Artist Sandra Lester believed she had found lasting love with the Yorkshire Ripper, and held hopes of a future marriage with him. She first contacted him at a low point in her life when she was coming to terms with the sexual abuse she suffered as a child.

An intense relationship followed through correspondence, but she was devastated when he refused to allow her to visit him and she found out that he was having similar relationships with a number of women.

Olive Curry, from Tyneside, did visit the killer at Broadmoor, however, and exchanged more than 500 letters with him. Her obsession dominated her life for ten years.

Diane Simpson, from Cheshire, exchanged more than 500 letters with Sutcliffe and spent more than 400 hours visiting him at Broadmoor.

The handwriting expert was involved in the original hunt for the killer, and tells the film-makers how Sutcliffe tried to manipulate her by hinting that he would confess to other crimes in order to maintain her interest.

American author Sheila Isenberg has studied the phenomenon of women who have relationships with notorious killers.

She claims that the common thread is a history of abuse and believes the relationships are like romantic novels or soap operas.

"A woman is living out this passionate, fantastic existence that has no basis in reality really, because if the man were not in prison they would have no relationship."

Former Chief Constable of West Yorkshire Keith Hellawell, who has spent many hours visiting Sutcliffe while investigating other crimes he may have committed, said the killer enjoyed the attention of the women, describing it as "just a game".

Controversy has surrounded previous television documentaries on the mass murderer who was convicted in 1981. Last year, ITV presented the first fictionalised account of the hunt for the Yorkshire Ripper.

Dear Peter ... Letters To The Yorkshire Ripper, is due to be screened next Wednesday at 10.35pm